TITANIUM-NIOBIUM-NICKEL HYDROGEN STORAGE ALLOY FOR BATTERY

Abstract: This invention relates to a titanium-niobium-nickel hydrogen storage alloy and more particularly, to the hydrogen storage alloy having a larger discharge capacity and light-weight secondary battery negative electrode material consisting of titanium-niobium-nickel, wherein it may be substituted with a variety af alloy atoms.

Description: TITANIUM-NIOBIUM-NICKEL HYDROGEN STORAGE ALLOY FOR BATTERY FIELD OF THE INVENTION This invention relates to a titanium-niobium-nickel hydrogen storage alloy and more particularly, to the hydrogen storage alloy having a larger discharge capacity and light-weight secondary battery negative electrode material consisting of titanium- niobium-nickel, wherein it may be substituted with a variety of alloy atoms. DESCRIPTION OF THE PRIOR ART Presently, a battery of small size and light weight has been common and to this end, it is imperative that the discharge capacity of electrode per unit weight should be increased, or the weight of alloy should be decreased, even though it has a same discharge capacity. As for the existing nickel/cadmium(Ni/Cd) secondary batteries which are in practical use, the price of cadmium has been as high as 4 times, thus raising the production cost. To make the matter worse, the environmental contamination due to a heavy metal cadmium from unrecovered batteries has been a severe social problem. In this context, the intensive research designed to substitute cadmium with other new materials has been under way from the middle of 1980s, and a nickel/metal hydride(Ni/MH) battery(U.S. patent No. 3,874,928, No. 4,004,943, No. 4,214,043 and Japanese unexamined patent No. 62-296365) was successfully developed. In 1991, a nickel/metal hydride secondary battery was already commercialized in both U.S. and Japan. The electrode reaction principle of nickel/metal hydride secondary battery is may be summarized as follows: when the battery is discharged, hydrogen atoms within the hydrogen storage alloy binds with OH " in electrolyte to form water and hence, electrons move to positive electrode through external circuit. When the battery is charged, H 0 in electrolyte is decomposed into hydrogen ion (H + ) and OH " , OH " remains in the electrolyte and hydrogen ion binds with electrons flowing from the outside. Then, the hydrogen atoms itself bind with hydrogen storage alloy so as to store the hydrogen within the alloy. This principle is based upon the fact that the hydrogen storage alloy is very stablized in alkaline solution, or upon the reversible property to readily absorb or release a sufficient amount of hydrogen. Compared with the existing nickel/cadmium battery, the hydrogen storage alloy has nearly similar battery properties, but the battery capacity increases as much as 1.5-2.0 times and its charging rate is as fast as more than two times. The property of secondary-battery hydrogen storage alloy greatly differs in terms of the kinds of alloy. Roughly, the hydrogen storage alloy having a plateau pressure of 1.00-0.01 atmospheric pressure at - 10~40°C (Proc. Int. Sym. Hydrides for Energy Storage, Geilo, Norway, 1977, 261). Presently, some hydrogen storage alloys having said property include lanthanum(La), neodymium(Nd), nickel(Ni), cobalt(Co) and aluminium(Al) [U.S. patent No. 4,487,817], Mischmetal . Mn, unpurified base alloy mixed with rare earth metals), manganese(Mn), nickel(Ni), cobalt(Co) and aluminium(Al) [Japanese unexamined patent No .61- 132501 , No .61-214360 and No.61-43063], titanium (Ti), vanadium(V), nickel(Ni) and chromium(Cr) [U.S. patent No. 4,551,400] and zirconium(Zr), vanadium(V) or nickel(Ni) [Int. Sym. on Metal Hydrogen System, Banff, Canada (1990)]. Among said alloys, the La-Ni electrode showed most severe degradation of electrode capacity due to the charge/discharge cycle in alkaline electrolytefJ. Less-Common Metals, 181(1990) 193 and 155 (1989) 119]. To comply with this matter, the substitution of nickel with cobalt or aluminum atom extends the life of electrode more or less, but the discharge capacity of electrode is on the contrary decreased from 372mAh/g to 250mAh/g. In this respect, the intensive research designed to develop a new electrode material with a larger discharge capacity and to extend the life of electrode has been made hitherto and as a result, the zirconium hydrogen storage alloy, having a discharge capacity of 300 - 400mAh/g as well as less discharge capacity despite its use 500 times or more, was successfully developed. However, the zirconium hydrogen storage alloy has recognized a disadvantage in that its large volume makes it difficult to move. Accordingly, the inventors selected some materials consisting of titanium, niobium and nickel as hydrogen storage alloy, being characterized by having a larger hydrogen storage alloy and light-weighed alloy and sought to substitute it with other alloy. Thus, as a result of intensive endeavours to develop the hydrogen storage alloy for nickel-metal hydride battery, the inventors have completed this invention in the long run. SUMMARY OF THE INVENTION Therefore, the object of this invention is to provide the titanium-niobium-nickel hydrogen storage alloy having a larger discharge capacity and light-weight material for secondary battery negative electrode. This invention is characterized by the titanium-niobium- nickel hydrogen storage alloy for battery having the following scope of composition. (Ti 0.4 Nb 0.6 ) 1 . Jt Ni x (wherein, 0.3 <X<0.4) Also, this invetnion includes the hydrogen storage alloy having the following scope of composition as one modified from the above hydrogen storage alloy, wherein said titanium(Ti) and niobium(Nb) is partially substituted with zirconium(Zr) and vanadium(V) respectively, and wherein nickel(Ni) is partially substituted with manganese(Mn), cobalt(Co) and chromium(Cr) respectively. (Ti 0 . 3 Nb 0 . 3 Zr ( , 4 . x V x ) ( , rι ( Ni 1 . y . z . Λ Mn ) , Co z CrA)o.r J (wherein, 0.1<X< 0.3, 0.05<Y,Z,A< 0.3 ) BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is the X-ray differaction pattern of an alloy comprising the composition formula of (Ti () 4 Nb O H ) 1.x Ni x (X=0.0, 0.1, 0.4, 0.5). Fig. 2 is the pressure-composition-temperature curve of an alloy comprising the composition formula of (Ti α4 Nb ϋ6 ) 1 . x Ni x (X=0.0, 0.1, 0.4, 0.5). Fig. 3 shows the theoretical discharge capacity and actual discharge capacity of an alloy comprising the composition formula of (Ti ( , 4 Nb ( , H ) 1 . x Ni x (X=0.0, 0.1, 0.4, 0.5). Fig. 4 is the pressure-composition-temperature curve of an alloy comprising the composition formula of (Ti 0 . 3 Nb a4 Zr 0 . 3 ) 0 . 5 Ni 1 . x . y Mn x Cr y . Fig. 5 is the discharge curve of an alloy comprising the composition formula of (Ti () 3 Nb 04 Zr () 3 ) () 5 Ni 1 . x . y Mn x Cr y . Fig. 6 is the pressure-composition-temperature curves of alloys comprising the composition formulae of following : A : (Ti ϋ.3 Nb α4 Zr αs ) αB Ni ( , 4 Mn ttl . B : (Ti 0.3 Nb α2 V llJ ,Zr ϋ.3 ) ϋ.rι Ni 0.4 Mn αl . C : (Ti 0 . 3 Nb ().4 Zr ( , 3 ) ( , rι Ni ( ,., rι Co (U)rj Mn 0 1. Fig. 7 is the discharge curves of alloys comprising the composition formulae of following : A : (Ti ϋ . 3 Nb α4 Zr ( , 3 ) l , r> Ni„. 4 n αlι B : (Ti 0.3 Nb α2 Zr ( , J ,)„ .rι Ni 0 . 4 Mn ttl, C : (Tϊ ϋ . 3 Nb l , .4 Zr,, Λ ),, . r,Ni ( , 3r ,Co ( , ϋ5 Mn l ,. 1 . Fig. 8 is the pressure-composition-temperature curve of an alloy comprising the composition formula of (Ti ϋ.3 Nb (K2 V l)-2 Zr α3 ) 5 (NiMnCoCr) 5 . Fig. 9 is the discharge curve of an alloy comprising the composition formula of (Ti u 3 Nb ()2 V () 2 Zr () 3 ) 05 (NiMnCoCr) () 5 . DETAILED DESCRIPTION OF THE INVENTION This invention relates to a titanium-niobium-nickel hydrogen storage alloy having a larger discharge capacity, which can be used as a light-weight secondary battery negative electrode material consisting of titanium-niobium-nickel, wherein titanium and niobium may be partially substituted with zirconium and vanadium selected from the alloy, and wherein nickel may be partially substituted with manganese, chromium and cobalt selected from the alloy. Said material is represented by the fomula, (Ti 0 . 3 Nb ( , 2 Zr ( , 5.x V x ) ( , s (Ni 1 . y .,. A Mιι y Co I Cr A ) ().0 (0.1 <X≤ 0.3, 0.05 <Y,Z and A≤0.3). The titanium-niobium hydrogen storage alloy absorbs about 2.6 wt. % of hydrogen, being equivalent to about 700mAh/g by calculation in terms of discharge capacity of electrode. Since a hydrogen overvoltage in electrolyte is high, said alloy cannot absorb hydrogens generated from electrolysis and instead, discharges them as a form of hydrogen gas. Thus, in order to manufacture the hydrogen storage alloy consisting of titanium-niobium-nickel(Ti-Nb-Ni) by adding nickel having less hydrogen overvoltage and in rather reasonable price, nickel is firstly substituted with an element selected from Ti ϋ 4 Nb 0 6 hydrogen storage alloy where titanium and niobium is comprising at atom ratio of 0.4:0.6 manufacture (Ti α4 Nb ϋ H ) 1 . x Ni x alloy. However, the titanium-niobium-nickel hydrogen storage alloy has reduced a hydrogen storage capacity drastically and this leads to significant reduction of discharge capacity in electrode. Also, said alloy has increased the balanced hydrogen pressure to some extent but the pressure is more or less low so as to apply it as an electrode material. The plateau pressure is inclined to be slanted. The results were shown in the X-ray differaction pattern of Fig. 1 where it shows that as the substitution amount of nickel increases(i.e. when X become large), the crystal structure will be changed from body-centered cubic in a single phase to body-centered cubic and hexagonal in two phases. Also, as for the (Ti () _ 4 Nb l ,_ β ) 1 . x Ni x hydrogen storage alloy, a pressure-composition-temperature (hereinafter called as "P-C-T") curve, showing the relationship between change of hydrogen composition and balanced hydrogen pressure according to absorption and discharge of hydrogen, was prepared in a constant temperature of 40" C. The results were shown in the Fig. 2 where it shows that as the amount increases, the absorption amount of hydrogen becomes reduced drastically. According to the Fig. 3, it shows a discharge capacity of hydrogen determined experimentally from an establishment of hydrogen-discharge capacity and actual electrode based upon theoretical calculation, using the absorption amount of hydrogen obtained from pressure-composition-temperature curve (P-C-T curve) of said Fig. 2. According to the Fig. 3, it shows that as the substituted amout of nickel is few(specifically, when X is less than 0.3), a theoretical discharge capacity is very large but an actual discharge capacity seems to be quite few, which may be explained as follows: because of too few nickel, electrons supplied from the outside may not contribute to absorption of hydrogen and they are chiefly used in producig hydrogen gas, thus leading to the lowerest charge efficiency. In case that the substituted amount of nickel exceeds 0.4, both theoretical discharge capacity and actual discharge capacity are reduced together, which may be explained as follows: despite sufficient charge, less absorption amount of hydrogen is responsible for the reduction of discharge capacity. Therefore, it is rather desirable that the composition of nickel in (Ti ϋ 4 Nb () H ) 1 . x Ni x should be changed within the scope of 0.3-0.4 according to the characteristics of electrode, taking change of temperature and current density into consideration. In consequence, whilst the theoretical discharge capacity of Ti ϋ 4 Nb ( , .β consisting of titanium and niobium is 700mAh/g, the discharge capacity of (Ti 04 Nb 0 H ) 1 . x Ni x , adding nickel as an alloy element, is lOOmAh/g. Thus, as nickel was substituted, the discharge capacity became reduced. More than 300mAh/g of discharge capacity should be at least required in making an electrode applicable in use. In order to increase the storage capacity of hydrogen and to extend the scope of slanted plateau pressure for its use as an electrode material, the substitution of titanium-niobium-nickel hydrogen storage alloy with some elements having good reactivity with hydrogen such as zirconium, vanadium, cobalt, manganese, chromium, etc. may lead to better increase of discharge capacity in electrode. In this respect, nickel was partially substituted with manganese and chromium, and zirconium was partially substituted with titanium and niobium. The results was shown in the P-C-T curve of (Ti 0 . 3 Nb α4 Zr α3 ) ( , rj Ni 1 . x . y Mn x Cr y of the Fig. 4. It is understood that when nickel was partially substituted with manganese and chromium, and zirconium was partially substituted with titanium and niobium at the temperature of 40°C, the storage capacity of hydrogen increased. As shown in Fig. 5, it is also understood that the increasing storage capacity of hydrogen may lead to increase of electrode discharge capacity in hydrogen storage alloy. However, its capacity of about 200mAh/g proved to have less discharge capacity. Therefore, in order to increase more balance pressure, niobium in the composition of (Ti u 3 Nb α4 Zr () 3 ) 05 Ni () 4 Mn 1 was partially substituted with vanadium, and nickel was partially substituted with cobalt respectively. As shown in Fig. 6, the substitution into vanadium(B curve) contributed much to increase of a balance-hydrogen-pressure but caused the reduction of hydrogen storage capacity, whilst the substitution with cobalt(C curve) has no had any change in hydrogen- storage-capacity but increasing a balance-hydrogen-pressure only. The results of such substitution effects were reflected in the change of electrode capacity in Fig. 7. The electrode substituted with vanadium showed nearly similar discharge capacity, whilst the electrode substituted with cobalt had an increase in discharge capacity. Through a careful observance that the effect of substituting alloy elements may lead to increase of discharge capacity, the secondary battery electrode hydrogen storage alloy of (Ti () 3 Nb () V () 2 Zr () 3 ) 0 r; (NiMnCoCr) ϋ 5 was successfully developed. The P-C-T curve of this alloy was shown in Fig. 8 and the discharge curve in Fig. 9. Hence, the discharge capacity was 300mAh/g, showing better results compared with the existing AB 5 type in discharge capacity of electrode (250mAh/g). Accordingly, the hydrogen storage alloy having a larger discharge capacity was successfully manufactured as a secondary battery negative electrode of this invention and said alloy has the following advantages: a) The discharge capacity is better improved than existing material; b) The size is smaller than that of AB 5 type alloy commercialized in Japan by increasing the discharge capacity per gram; Thus, the hydrogen storage alloy of this invention comprising said composition can be very widely and effectively used in the batteries of movable camera or electric automobile. Hereinafter, this invention may be described in EXAMPLES but this invention is not confined to the EXAMPLES. EXAMPLE 1 : Method to obtain the pressure-composition-temperature curve In order to manufacture the hydrogen storage alloy, the amount of each atom was determined by its relevant atom ratio to weigh the total weight by about 15g. Under the presence of argon, arc dissolution was performed. Hence, for the samples homogeneous improvement, the sample was solidified and then, the re-dissolution process by reversing the sample was repeated 4 - 5 times. By grinding the sample, it was put in reaction tube of 100-200 mesh and connected to Shivert's type high-pressure hydrogen appratus. For the sake of activation treatment, the inter-reaction tube was maintained at about 10-2 torr for 30 mins and then, hydrogen was added in about 20 atmospherical pressure without thermo- treatment. The absorption of hydrogen was completed within one hour. By maintaining the inter-reaction tube in a vacuum state once again, all hydrogens present in the interior of the sample was discharged. By repeating the absorption-release process of hydrogen 3 - 4 times, the absorption-release process of hydrogen was completed within several minutes. Meantime, after said activation treatment, a hydrogen, injected apparatus including the reaction tube was maintained in a constant temperature, using an automatic temperature modulator and under a constant temperature, the balanced hydrogen-pressure curve was obtained according to hydrogen composition in the absorption-release of hydrogen. And from this curve, some data on absorption amount of hydrogen and plateau pressure was also available. EXAMPLE 2 : Measurement for discharge capacity Pure metals were weighed in desired ratio and under the presence of argon, they were dissolved to manufacture a sample. By grinding the manufactured alloy mechanically, some materials such as copper, nickel powder and teflon powder were mixed in appropriate quantity and then, the molding by adding pressure was made to obtain the desired electrode. This electrode was immersed in 30wt.% of potassium hydroxide electrolyte and a half of battery in opposite electrode was organized by using platinum or nickel. Between two electrodes, a constant current should flow with amperemeter to inject hydrogen within electrode and when discharged, both electrodes were changed. Hence, in order to determine the voltage of hydrogen storage alloy electrode, saturated calomel electrode and oxidized mercury electrode (Hg/HgO) were used as comparative electrode. When the discharge capacity is discharged in a constant current, time and current(mA) was mutiplied until the voltage reaches -0.75V in proportion to the saturated calomel electrode and then, divided with a weigh(g) of hydrogen storage alloy. Thus, the capacity was expressed as ampere capacity per unit weight.

Claims: WHAT IS CLAIMED IS : 1. A hydrogen storage alloy for battery having the following scope of composition. (Ti .Nb. ^Ni,. (wherein, 0.3 <X<0.4 ) 2. A hydrogen storage alloy having the following scope of composition as one modified from the hydrogen storage alloy of the above claim 1, wherein said titanium(Ti) and niobium(Nb) is partially substituted with zirconium(Zr) and vanadium(V) respectively, and wherein nickel(Ni) is partially substituted with manganese(Mn), cobalt(Co) and chromium(Cr) respectively. (Ti ϋ . 3 Nb ϋ . 3 Zr ( , 4 . x V ) 0.0 (Ni 1 . y . I . A Mn y Co z Cr A ) 0 . 6 (wherein, 0.1 <X<0.3, 0.05<Y,Z,A<0.3)

Inventors: BAE DO IN, KIM YOUNG WOO, LEE JAE YOUNG, LEE JON HA, BAE, DO, IN, KIM, YOUNG, WOO, LEE, JAE, YOUNG, LEE, JON, HA
Applicants: BAE DO IN, HYUNDAI MOTOR CO LTD, KIM YOUNG WOO, LEE JAE YOUNG, LEE JON HA, BAE, DO, IN, HYUNDAI MOTOR COMPANY, KIM, YOUNG, WOO, LEE, JAE, YOUNG, LEE, JON, HA
Application year: 1994
Main classification: H01M4
IPC codes: C01B3, C22C19, H01M4